In particular, the present invention relates to a plinth with exposed horizontal reinforcing bars, i.e. at right angles to the direction of casting of the concrete, which make it possible, as will become clear hereinbelow, to form an optimal and advantageous connection with the corresponding pillars.
In the construction of buildings or of other building structures from concrete, the foundation elements, i.e. the base plinths and the corresponding pillars, are nowadays made and coupled together with a number of different traditional methods.
In the design of prefabricated structures, connections play an essential role in terms of seismic resistance of the entire building. Precisely for this reason, connections as classified as a function of their characteristics. A first distinction can be made on the basis of the position and function of the connections inside the structure, by defining the critical area as “the region of a primary seismic element where the most unfavorable combination of the effects of the actions arise, and where plastic hinges can form”.
The connections can be arranged outside the critical regions, i.e. they must be positioned at a distance from the critical section at least equal to the maximum dimension of the transverse cross-section, and they do not influence the energy dissipation capacity of the structure. If they are instead arranged inside the critical regions, then there are two connection possibilities.
The first possibility comprises the use of connections that are suitably overdimensioned with respect to the rest of the structure, so that in the design seismic situation they remain elastic, while the nonelastic behavior occurs in the other critical regions. In this case, the reinforcements must be anchored outside the critical area and the reinforcement of the critical area must be anchored outside the connection.
The second possibility comprises the use of a connection inside the critical area with significant ductility that allows plastic rotations.
The first development of a prefabricated foundation was the socket plinth, which is very similar to a plinth cast in-situ, but with a hole to receive the prefabricated pillar at its center. Once the foot of the pillar is inserted in the socket, a casting of grouting with shrinkage-compensating concrete is necessary, which creates the solid medium between the plinth and the pillar, creating a permanent joint for the structure.
In a second type of connection, there are bars which protrude below the pillar and corrugated tubes embedded in the foundation plinth.
Connection with protruding bars can be used in foundations that are prefabricated (such as plinths) or cast in-situ. The fastening plate is a metal device which is embedded in the casting of the foundation, and its purpose is to support the pillar during the installation step and to allow it to be grouted with the foundation. It is constituted by a metal frame, which connects a series of corrugated tubes that are closed at the base, the function of which is to create compartments in the foundation, into which the matching bars of the pillar will be inserted.
The prefabricated pillar is therefore made with longitudinal bars exiting from the base section so as to be inserted into the holes of the corrugated tubular elements. Once the pillar is inserted, filling is carried out and a formwork is built for the completion casting with non-shrinking mortar in the corrugated tubes.
In a third type of connection between plinth and pillar, bolted column shoes are arranged on the base of the pillar.
The shoes are angled metal elements which are inserted at the foot of the pillar during casting, with an insert to leave the part above the shoes empty. In the plinth, corresponding anchor bolts, in the form of threaded steel elements with improved adherence, are anchored.
The pillar is anchored by clamping by way of nuts during the mounting. Finally, a supplementary casting is done using shrinkage-compensating mortar.
The anchor bolts in the foundation must be positioned exactly as specified in the design drawing. The use of templates is recommended to ensure that such anchorages are exactly positioned according to the dimensioning and in order to prevent shifts during the casting and vibration of the concrete.
The mounting steps are carried out in this order: once the pillar is ready and the anchor bolts are fixed in the foundation, remove the template, insert the metal plates for the mounting, and position the caps on the anchorages. Then lower the pillar, remove the caps and screw the nuts onto the anchor points, thus adjusting the vertical orientation of the pillar. At this point the pillar is immobilized in the foundation and the spaces left by the inserts and the joint between the foundation and the pillar must be filled with the mortar. This filling can be done by way of a tube left in the pillar or by way of a formwork around the joint.
Obviously it is also possible to provide both plinth and pillar directly in-situ.